1. Field of the Invention
The present invention relates to fluorescent latices exhibiting high quantum yields, very low detection thresholds for fluorescence and the constituent particulates of which incorporate at least one hydrophobic fluorochrome.
2. Description of the Prior Art
Latices are known to this art as aqueous dispersions of polymer particles, the size of which generally ranges from 0.1 microns to several microns. Taking account of their particulate nature, latices have a high specific surface which is exploited to advantage in a wide variety of applications and, in particular, in the paint, magnetic tape and recording industries and in various fields of biology.
In biology and more particularly in the field of immunology, conventional techniques for quantitative determinations employ latices as a support for markers of the enzyme or radioisotope type to permit the quantitative determination of the species present in the mixtures to be analyzed.
This technique of quantitative determination by molecular labelling using a radioactive isotope is extremely precise and reliable and has a high qualitative sensitivity. However, it has several disadvantages associated with the dispersion of the radioactive sources, prolonged exposure of the personnel, variation with time of the emission of the source relative to the half-life of the element, and most importantly, to the necessity, upon completion of the analysis, to isolate the free reactants from the complexed reactants. Radioactive emission is, in effect, completely insensitive to the environment of the label.
For the reasons given above, the technique of analysis by fluorescence represents the most efficient alternative for the replacement of these conventional labels.
The advantages of fluorescent labelling, in comparison with radioactive labelling, are manifold. The risk of radioactive exposure is zero. Fluorescent labelling exhibits an excellent stability with time and, significantly, it provides a more refined response due to the specificity of fluorescent emission to certain environmental parameters. Thus, its use does not require post-analysis separations.
The practical use of fluorescence, in immunological quantitative determinations, thus remains simply subordinated to a demand for quantitative sensitivity. Its sensitivity must be comparable with that of radioactive labelling which entails operating at concentrations ranging from 10.sup.-12 to 10.sup.-15 mol of particles per liter.
Currently, it is the level of its sensitivity that limits the use of analytical techniques based on fluorescence.
Fluorescence, resulting from simple molecular grafting, exhibits insufficient sensitivity for the purpose of a generalized practical application. It is difficult to detect same when the concentration of the entities present in the medium of analysis is less than 10.sup.-9 mol/liter.